The present invention relates to remote visual landing aid systems for guidance of aircraft during final approach and in particular to an active, electro-optical display system for enhancing visual cueing information projected to the pilot of an approaching aircraft from the point of intended landing on an airport runway. Successful aircraft landings, particularly night time operations into short runways and into airports with long, overwater approach patterns extending into a surrounding body of water, necessitate the highest degree of safety and control to ensure maximum protection for passengers, cargo and aircrew.
In seeking to provide that degree of safety and control, passive visual landing and approach lighting systems were developed to guide pilots on approach to runways, particularly during the hours of darkness. One such visual landing aid system is the International Civil Aviation Organization (ICAO) worldwide standard for commercial aircraft operations, the Visual Approach Slope Indicator (VASI) system. The VASI provides passive glideslope displacement information (position) through color-coded projected beams of light which indicate to the pilot whether the aircraft is above, below or correctly on the proper glide path angle.
A newer passive visual landing aid, the Precision Approach Path Indicator (PAPI) is in widespread use and operates in accordance with the same basic optical projection principles as does the VASI.
While the angular elevation information provided by VASI is valuable as an altitude reference, the system has proven to be limited in usefulness in providing trend or direction and rate of change information relative to the optimum glideslope. Because the information provided by the VASI is of zero order (displacement only) there are substantial time lags between aircraft control inputs and subsequent observable changes in the VASI display. In particular, relatively large descent rate perturbations are required before noticeable color changes are apparent. Trend or rate information is thus derived only through a time history (several seconds) of observing the display. From a human factors engineering perspective, the piloted landing process can be described as a second or third order closed loop manual control task. For maximum effectiveness, a visual display for accurate closed-loop control should more closely simulate the control order and dynamics of the feedback loop between pilot control input and aircraft dynamic response. It is thus advantageous to augment position information with instantaneous velocity and acceleration cues.
Furthermore, the inherent limitations of the VASI are accentuated at night, when there is a severe reduction in the natural visual cues used by the pilot to assist in estimation of azimuth and elevation rates of change. The nightime reduction in these natural cues used by the pilot, such as expansion pattern relationships, surface texture gradients, peripheral streaming, and horizontal field-of-view discrimination adversely affects the pilot's perceptual capabilities rendering accurate control of azimuth and elevation rates far more difficult than during daylight. In fact, the apparent tendency to "duck under" the VASI glideslope at night on long, overwater approaches has been documented as a contributive factor in several commercial air transport landing accidents.
The present invention attempts to overcome this deficiency of previous passive visual landing aids by adding active, real-time, higher order derivative information to the zero order VASI position information (passively displayed for fail safety considerations) in an integrated format that minimizes distraction and reduces pilot workload.
Accordingly, it is thus a general purpose and object of the present invention to provide an improved visual landing aid system for remotely guiding the descent approach of a fixed-wing aircraft to a conventional airport runway, in such a manner that does not add significant vertical obstructions to the landing area.
Another object of the present invention is to provide an optical display system for remote guidance of aircraft landings, wherein visual presentation of information more closely simulates the control order and dynamics of the actual feedback loop between the pilot command and the aircraft response.
Still another object of the present invention is to provide an active optical display system that augments the passive VASI or PAPI systems presently used to guide aircraft landings by enhancing the visual cueing information presented to the pilot through the addition of a continuous visual indication of the instantaneous magnitude and direction of aircraft descent rate relative to the optimum descent rate (that which maintains or intercepts the desired glideslope angle).
Another object of the present invention is to provide a continuous indication of instantaneous velocity change along the flight path (deceleration or kinetic energy dissipation) to provide enhanced wind shear warning and detection.
Still another object is to provide a continuous indication of instantaneous lateral drift rate relative to the runway centerline.
A further object of the present invention is to provide a remote visual landing aid for aircraft approaches that facilitates tracking of the desired glideslope during night operations so that the risks of landing accidents are significantly reduced.